I came across a lot of similar example for foreign key CREATE TABLE orderinfo ( orderinfo_id serial , customer_id integer NOT NULL, date_placed date NOT NULL, date_shipped date , shipping numeric(7,2) , CONSTRAINT orderinfo_pk PRIMARY KEY(orderinfo_id), CONSTRAINT orderinfo_customer_id_fk FOREIGN KEY(customer_id) REFERENCES customer(customer_id) ); instead of let customer_id being type as integer, can i let it be serial? is there any difference? if the table referenced by customer_id is having primary key typed big serial, customer_id shall be declared as bigint ? Thanks -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general